A current DC/DC converter, as shown in FIG. 1, comprises a transformer T, a switching transistor S1, a diode D, a filter capacitor C and a load R. The transformer T comprises a primary winding N1, and a secondary winding N2. A first terminal of the primary winding N1 of the transformer is connected to a DC input source V, a second terminal of the primary winding N1 is grounded through a switching transistor S1, a first terminal of the secondary winding N2 is connected to an anode of the diode D, a cathode of the diode D is connected to first terminals of the filter capacitor C and the load R, and a second terminal of the secondary winding N2 is connected to second terminals of the filter capacitor C and the load R. In cooperation with the switching transistor S1 which is under control of a PWM pulse wave, the DC/DC converter delivers energy of the DC input source V to the load connected to a secondary terminal through the transformer. However, the DC/DC converter as described above can only implement single power supply. If it is intended to implement power supply of two DC input sources, two DC/DC converters as described above are required. In the prior art, a two-input DC converter circuit is also proposed, for example, in the patent application with Publication No. CN102097943A entitled “two-input DC converter”, the proposed two-input DC converter can implement power supply of a two-input power source; however, a circuit structure thereof needs to use more switching transistors, so that many components are used and control is complicated, thereby resulting in a complicated circuit structure and high circuit cost.